Our long-term objective is to elucidate the mechanisms that regulate the compartmentalization of plasma membrane of plasma membrane proteins on mammalian spermatozoa and to determine the roles that domain-specific spermatozoal plasma membrane proteins play in reproductive biology. We have recently identified an integral plasma membrane protein of the rat spermatozoon called CE9. Although originally compartmentalized to the posterior tail plasma membrane domain of testicular spermatozoa, this transmembrane glycoprotein redistributes to the anterior tail plasma membrane domain during epididymal maturation. The redistribution of CE9 is preceded y the endoproteolytic removal of about 40% of its extracellular domain in an early segment of the caput epididymidis. Our aims of this first project period are to begin to elucidate the mechanisms that regulate the compartmentalization of CE9 and to attempt to establish the generality or specificity of these phenomena, both among other the spermatozoa of other species and among other rat spermatozoal plasma membrane proteins. We are proposing to: (a) use immunocytochemistry to determine how the unusual posterior tail-specific localization of CE9 arises during spermatogenesis; (b) use immunogold labeling and electron microscopy to determine whether the localization of CE9 is consistent with the annulus acting as a barrier to the lateral diffusion of CE9 within the spermatozoal plasma membrane; (c) characterize a 50 Kd protein that can be crosslinked to CE9 on the surface of the rat epididymal spermatozoon and my therefore play some role in the compartmentalization or function of CE9; and (d) to assess the generality or specificity of the phenomena surrounding CE9 by using antibody and CDNA probes to first identify and then compare the processing and localization of CE9 homologues on the spermatozoa of other species and by using monoclonal antibodies to identify and characterize additional plasma membrane proteins that share the pattern of compartmentalization with CE9 on the tail of the rat spermatozoon or otherwise show interesting localizations.